Probing Molecular Mechanisms of Self-Assembly in Metal-Organic Frameworks: A MD Simulation Study
Abstract
Metal-organic framework materials (MOFs) are a class of porous, solid-state materials, important to many applications. Although MOF synthesis has received considerable attention, very little is known about the mechanisms of self-assembly of MOFs. The primary goal of this thesis is to provide molecular level insights into the mechanistic details of the self-assembly process for an archetypal Zn-carboxylate MOF. In this thesis, simplified atomistic models representing Zn-ions, carboxylate ligands, and solvents were designed and validated against characteristic parameters for a key MOF structure. The Zn-ion models were further benchmarked by comparing the potential of mean force profiles for Zn-Zn and Zn-carboxylate oxygen generated from classical simulations to those generated from ab initio simulations. An extended cationic dummy atom (ECDA) Zn-ion model combined with an all-atom BDC ligand model and simple dipolar solvent model are found to reproduce key structural motifs anticipated for the archetypal Zn- carboxylate MOF system. The efficiency of these models provided access to relatively long time scale ordering processes during simulations. While a simple dipolar solvent model was found to exhibit structural behaviour similar to that of a more realistic DMF solvent, the former demonstrated a significantly faster rate of structural reorganization. A continuum solvent model was observed to exhibit structural behaviour similar to that of the dipolar solvent model, although with this model key structural motifs appear relatively less stable. The effect of system compositions, both increased concentrations and carboxylate ligand ratios, on structural behavior of the systems were also investigated. Through extensive sets of simulations, fundamental insights that elucidate key aspects of the self-assembly mechanism for MOFs are provided. An important finding of this study is the characterization of a stochastic and multistage ordering process intrinsic to self-assembly of the Zn-carboxylate MOF system. A variety of transient intermediate structures consisting of various types of Zn-ion clusters and carboxylate ligand coordination, and featuring a range of geometric arrangements, are observed during structural evolution. The general features deduced here for the mechanism of the self-assembly of this archetypal MOF system expose the complexities of the various molecular level events that can occur during different stages of structural evolution.
Description
Keywords
Education--Sciences, Chemistry--Physical
Citation
Biswal, D. (2017). Probing Molecular Mechanisms of Self-Assembly in Metal-Organic Frameworks: A MD Simulation Study (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27439